Rod (unit)

The rod is a unit of length, equal to 5.5 yards, 11 cubits, 5.0292 metres, 16.5 feet, or of a statute mile. A rod is the same length as a perch and a pole. The lengths of the perch (one rod) and chain (four rods) were standardized in 1607 by Edmund Gunter.The length is equal to the standardized length of the ox goad used by medieval English ploughmen; fields were measured in acres which were one chain (four rods) by one furlong (in the United Kingdom, ten chains).Because the furlong was "one plough's furrow long" and a furrow was the length a plough team was to be driven without resting, the length of the furlong and the acre vary regionally, nominally due to differing soil types. In England the acre was 4,840 square yards, but in Scotland it was 6,150 square yards and in Ireland 7,840 square yards. In all three countries, fields were divided in acres and thus the furlong became a measure commonly used in horse racing, archery, and civic planning.
See more at Wikipedia.org...